Air heating device



Jan. 14, 1936; T. J. TULLY ET AL AIR HEATING DEVICE Filed May 14, 1934INVENTORS Thomas J 7Z1/l Roberf B. Jacon y M ATTORNEW Patented Jan. 14,1936 UNITED STATES PATENT OFFICE AIR HEATING DEVICE corporation of OhioApplication May 14, 1934, Serial No. 725,547

14 Claims.

()ur invention relates to air-heating devices. It has to do, moreparticularly,-with a portable air-heating device which may be readilyhandled and which is of the type commonly referred to as air-heatingguns. This device which we have provided is particularly applicable toremoving solidified or stiff oils and greases from crank cases,transmissions and differential cases or other gear boxes of automobilesor the like.

However, our device may be used for many other purposes.

There have been several types of air-heating devices of the general typeindicated provided in the prior art. However, these prior art deviceshave not been entirely satisfactory. Probably the greatest disadvantageof these prior art devices resides in the fact that they are complicatedin structure and are, therefore, difiicult and expensive to make, andare very diilicult to assemble which also adds materially to the cost ofmanufacture.

These prior art devices have, also, not been entirely satisfactory inoperation. In the past, none of these devices have been provided withadequate means for insulating the outer casing and the handle, which areusually made of metal, from the heat developed in the gun, with theresult that the said outer casing and the handle might become so hot asto burn the operator when he touches the gun. It has been proposed inthe prior art to make the handle member of bakelite or some othermaterial which would not conduct heat. However, when the handle is madeof bakelite or the like, it will become cracked or broken readily sincethese guns are usually subjected to hard usage and may be dropped fromtime to time. Still another disadvantage of prior art devices resides inthe fact that the heating elements of these devices are usually notadequately protected from shocks and jars. Also, these prior art devicesare usually of such a nature as to be expensive to operate.

One of the objects of our invention is to provide a heating device ofthe type indicated which is very simple in structure and which is ofsuch a that it may be readily assembled and, consequently, which can bemanufactured and sold at a comparatively small cost.

Another object of our invention is to provide an air-heating device ofthe type indicated which will be very economical to operate and whichwill function in a very efficient and satisfactory manner.

Another object of our invention is to provide an air-heating device ofthe type indicated which can be made practically entirely of metal andwill thereby be very sturdy and which will be provided with suitableinsulating means so that there will be no danger of the operator beingburned when handling the said device.

Another object of our invention is to provide an air-heating device ofthe type indicated which will be provided with a heating element soincorporated in the device that it will be protected from shocks andjars.

Another object of our invention is to provide a heating device of thetype indicated which is provided with a safety device that will obviateany danger of the device becoming overheated or excessively heated.

In its preferred form, our invention contemplates the provision of aheating device for the purposes indicated which is provided with meansfor conducting air therethrough and with means for heating the air as itpasses through the device. The air is caused to travel a comparativelygreat distance so that it will be adequately heated before leaving thedevice. The heating means is disposed in a housing which is made ofmetal and which has a suitable metal handle member connected therewithand the housing and handle member are insulated from the heating meansat all points so that there will be no danger of the outer casing orhandle member becoming so hot that it will be impossible for theoperator to handle the device. A safety switch is provided so that theheating means will function only when air is being applied to the deviceand, consequently, there will be no danger of the device becomingover-heated.

Many other objects and advantages will appear from the followingdescription.

The preferred embodiment of our invention is shown in the accompanyingdrawing wherein similar characters of reference designate correspondingparts and wherein:

Figure 1 is a longitudinal section of an airheating device made inaccordance with our invention.

Figure 2 is a detail in section illustrating an air injector which wepreferably incorporate in our device and, also, illustrating theautomatically operative safety switch which controls operation of theheating element of our device.

Figure 3 is a perspective view of certain members of our device whichare used in assembling the various parts thereof.

Figure 4 is a perspective view of a tube which is adapted to surroundthe heating element of our device.

Figure '5 is a diagram of the circuit for the electrical heatingelement.

Figure 6 is a perspective view, partly broken away, of our air-heatingdevice.

Figure 7 is a diagrammatic view illustrating how our air-heating devicemay be used for cleaning a gear box or the like.

With reference to the drawing, we have illustrated our air-heatingdevice as being in the form of a gun. Our device comprises a handlemember l which is of the pistol type. This handle member is providedwith a flange 2 at its forward end which is adapted to be bolted to aflange 3, formed on the rear end of the main casing d of the heatingdevice, by means of screw bolts 5 passing through corresponding threadedopenings in flanges 2 and 3.

The casing 4 is of substantially cylindrical form, as illustrated in thedrawing, and its rear end is open as indicated. This casing ispreferably made of metal and both its inner and outer surfaces arebright and polished. The forward end of the casing converges asindicated at 6 and has a substantially flat forward end I of annularform. This flat end I has a square opening 8 formed therein for apurpose which will be described subsequently.

The handle member I, as shown, is of such a type that it may be readilygripped in the hand. It is preferably made of metal although it might bemade of other suitable material. The casing i is also preferably ofmetal. The handle member I has a passageway 9 formed therein whichextends from the lower end thereof upwardly through the handle memberand communicates at its upper end with the chamber formed within thecasing 4. An electrical conduit I0 is adapted to be passed through thispassageway 9 and is adapted to supply electrical current to a heatingelement which will be subsequently described.

The handle member I further has a vertically extending air passageway Il formed therein. The lower end of this passageway H has a couplingmember 12 threaded thereinto which is adapted to be used for connectinga hose member (not shown) thereto. This hose member is adapted to beconnected to a tank or the like containing asupply of compressed air.The coupling 52 has a screen member l3 on its upper edge which willprevent foreign matter which might be carried by the air stream fromentering the passageway ll.

Adjacent the upper end of the passageway H, a forwardly extending airpassageway 16 is provided, the rear end of which communicates withpassageway II. This passageway extends entirely through the handlemember and its forward end is open as indicated. The forward portion ofthis passageway M has a safety switch l5 mounted therein. This switch ismounted in a slightly enlarged portion 16 of the passageway id and isprovided for automatically controlling the supply of electric current tothe heating element of our device.

This safety switch 15 is of such a type that it is automaticallyoperated by air pressure passing through passageway H and intopassageway it. It will only complete the circuit to the heating elementwhen air under pressure is in passageways l l and I4.

This safety switch i5 comprises a plunger which is composed of a bodyportion ll made of some suitable material which will not conductelectricity. This member ii is of less diameter than the enlargedportion I 6 of passageway 14. The rear end of this member ll has a metalbearing member l8 secured thereon by means of a bolt member [9 which isscrewed into member ii. The bearing member I8 is of slightly lessdiameter than the enlarged portion it of passageway i i. A disc Zii ofnon-conducting material is held against the rear surface of the bearingmember 'IS by means of the bolt I59 and a washer 2!. This disc 28 is ofsubstantially the same diameter as member l8 and will contact with theshoulder 22, formed at the beginning of the enlarged portion it, whenthe plunger of the switch is in its rear position as indicated in Figure2.

The member I! of the switch has a compression spring 23 disposed insurrounding relation thereto. 7 The rear end of this spring will abutthe bearing member I8. The forward end of this spring will abut a collarmember 24 disposed at the forward end of the passageway It. This collarmember is secured in the position indicated in a suitable manner and ismade of non-conducting material. It has an opening 25 extendingtherethrough. A contact member 26 made of metal is adapted toreciprocate in this opening. This contact member is preferably larger indiameter at its center portion than at its end portions as shown. It ismounted on the forward end of member I! by means of a bolt 27.

The forward side of the collar member 24 has a contact member 28 mountedat each side of the opening 25 formed therein. These contact members areresilient and extend over the limits of the openings 25. They extendforwardly and are directed towards each other as indicated in Figure 2.Each of these contact members is connected into the electrical circuitfor the heating element as will be described later. As indicated in thisfigure, when the plunger of the switch is in its rearmost position,where it is normally held by spring 23, the contact member 26 will bedisposed as indicated and there will be no electrical connection betweenthe two contacts 28. However, if the plunger is moved forwardly, thecontact member 26 will move between the two contacts 28, as indicated bythe dotted lines, which will contact firmly therewith. Thus, electricalconnection between the two contacts 28 will be established.

The plunger of the switch will normally be held in the positionindicated by the full lines in Figure 2 by the spring 23. However, ifair under pressure is flowing through passageway II and passageway I4,the plunger of the switch will be moved forwardly as described andcomplete the circuit between the two contacts 28. However, if the airpressure in the passageways II and I4 falls below a predetermined degreeor is eliminated, the plunger will be returned to its rearwardmostposition and the electrical circuit will be broken. Thus, the only timethat electrical current can be supplied to the heating element will bewhen there is a desired amount of air pressure in passageways H and i4.

We prefer to have our air-heating device connected to a supply ofcompressed air as indicated and which is obtainable at all gasolinefilling stations or the like. However, in using our device, it isusually not necessary to have the air under pressure equal to that inthe tank from which it is taken. Therefore, we have provided means forreducing the pressure of the air supplied through passageway II. We havealso provided means for taking in air from the atmosphere in addition tothat taken through passageway so that it will not be necessary to use anundesirable amount of air taken from the tank to which the passageway IIwill be connected. This means comprises an air injector which will nowbe described.

This air injector is formed in a passageway 29 formed in the upperportion of handle member and having its rear end communicating withpassageway I I and its forward end communicating with the chamber formedwithin casing 4. The rear end of passageway 29 has a shoulder 30 formedtherein as shown. Adjacent this shoulder 30 and forwardly thereof, thepassageway 29 has a nozzle member 3| threaded thereinto. This shoulderlimits rearward movement of member 3|. This nozzle member has an airdischarge orifice 32 formed therein which is an approximate venturi.Atthe forward end of the passageway 29, a second nozzle member 33 isthreaded thereinto. This nozzle member 33 is longer than the member 3|as shown and its rear end is spaced a considerable distance from theforward end of nozzle 3|. This nozzle member 33 also has a dischargeorifice 34 extending entirely therethrough and which is in the form ofan approximate venturi. It will be apparent that a chamber 35 is formedin passageway 29 between these two nozzle members.

This chamber 35 has an opening 36 formed in one wall thereof whichopening communicates with the atmosphere. The forward end of nozzlemember 3| extends slightly past the rear edge of opening 36. Theorifices 32 and 34 are substantially in alignment and the forward end oforifice 32 is of slightly less diameter than the rear end of orifice 34.

This injector will function in the usual manner. The air under pressurewill flow through nozzle member 3| and will be directed into nozzlemember 33 and will then be discharged therefrom into the chamber withincasing 4. Air will also be drawn in through the opening 36 from theatmosphere in a well known manner and this induced air will be carriedinto the chamber within casing 4. The pressure of the air dischargedinto the chamber within casing 4 will be much less than the pressure ofthe air in the passageway being reduced by passing through the injector.Furthermore, since the air under pressure is supplemented by induced airfrom the atmosphere, it will not be necessary to use an undesirableamount of air taken from the tank to which passageway I may beconnected.

The opening 36 not only serves as a means by which air may be drawn fromthe atmosphere but also serves as a safety valve which will prevent thebuilding up of an undesirable degree of pressure in the chamber Withincasing 4. The nozzle member 33 is so designed that when the pressurewithin casing 4 becomes too great the air will begin to back up throughthis nozzle member 33 and will pass to the atmosphere through theopening 36. In case it is desirable to ever build up a high pressure inthe chamber within casing 4, the opening 35 may be closed, for example,by placing the finger thereover. This will cause the building up of amuch greater pressure within the casing 4.

Centrally located within the cylindrical casing 4, is a heating element31. This heating element may be of any suitable type but preferablycomprises a porcelain core having heating coils wound therearound asindicated. The porcelain core has an opening extending longitudinallytherethrough and a bolt member 38 passes therethrough. This bolt memberis used to secure the heating element to a triangular member 39 whichwill be disposed at the rear of the chamber within casing 4 but will bespaced, as illustrated, from the forward end of the handle member Thistriangular member is made of some material which will not conduct heatand which is noncombustible. It will touch the casing 4 at three pointsas illustrated in Figure 6 but since it is composed of insulatingmaterial it will not conduct heat from the heating element to the outercasing. Also, due to its shape, air will be permitted to pass forwardlyof this member 39. Further, this member 39 is made of material which isflexible so it will serve as a cushion which Will minimize shocks andjars on the heating element. The contact members 28 on the collar member24 disposed adjacent the safety switch are connected into the electricalcircuit for the heating element 3'! by means of wires 40. The circuitfor the heating element is illustrated diagrammatically in Figure 5. Theforward end of the heating element is provided with a plurality ofoutwardly projecting leg members 4| which are spaced apart to permitpassage of air.

Directly surrounding the heating element 37, is a tubular member 42composed of suitable metal. The rear end of this member 42 is curledoutwardly as indicated at 43 and when our device is assembled thiscurled portion 43 will project beneath a flange 44 formed on the innerperiphcry of a ring 45. This ring 45 is fastened to the forward face ofmember 39 by means of screws 46.

It will be apparent that the legs 4| on the heating element will keepthe forward end of the body portion thereof spaced from the tube 42. Thetube 42 is provided with a plurality of small circumferentially spacedopenings 4'! at its rear end. It will be apparent that a chamber 48 isformed within tube 42 and around heating element 37.

Disposed in surrounding relation to the tube 42 is a second tube 49which will be spaced from the tube 42 and will form a chamber 50. Thistube 49 is held in spaced relation to tube 42 by its inwardly curledends. It has openings 52 similar to openings 4'! in its forward end. Athird tube 53 is disposed in surrounding relation to tube 49 and isspaced therefrom in a similar manner to form a chamber 54. A chamber 56is formed in surrounding relation to tube 53 by a tube 55 in a similarmanner. Tube 53 is provided with openings 51 at its rear end and tube 55is provided with similar openings 58 at its forward end. It will beapparent that the circumferential openings in each tube are at the endopposite to the end of the adjacent tube where the openings thereof arelocated. It will further be apparent that the only means which need beprovided to maintain the tubes in spaced relation to form the variouschambers are the inwardly curled ends of the tubular members. Thesetubular mem bers are preferably made of metal which has both its innersurface and outer surface polished for a purpose which will be broughtout later.

When the air flows within the casing 4, it is adapted to pass forwardlyalong the outer tube 55, to flow through openings 58 into the outermostchamber 55, to flow rearwardly through this chamber to the rear endthereof and then through openings 51 into the next adjacent chamber 54.Then, the air will flow forwardly through this chamber until openings 52in tube 49 are reached and will then flow therethrough into chamber 50.From chamber 50, it will flow through openings til into the chamber 48surrounding the heating element. It will be apparent that the air willbe caused to travel through a great distance before reaching the heatingelement. Thus, the air will be pre-heated before it reaches the heatingelement, since it will absorb heat from the various tubular memberswhich are made of metal. Furthermore, since the surfaces of thesetubular members are polished, they will serve as heat-reflectingsurfaces and will much more readily give oii their heat to the airpassing through the various chambers. Because the surfaces of thevarious tubes and the surfaces of easing 4 are polished, they will havea great insulating value. It will be apparent that the heat will notreadily pass outwardly through these members but will be reflected fromtheir inner surfaces back into the chambers. Further, since the outersurface of these members are polished, if the heat does pass into thesemembers, it will not be given oiT readily. Also, since we have providedseveral chambers which will have air passing therethrough, the outercasing 4 will not be affected to any material degree by heat radiatingfrom the heating element.

The rear ends of the various tubular members will contact with the metalring 45 which is fastened to the triangular member 39. These varioustubular members are held in place by a disc 59 of metal which issubstantially of the same diameter as the outermost tube and which isheld against the forward ends of the tubular members as shown inFigure 1. The disc will close the forward ends of any of the variouschambers formed by the tubular members which are not otherwise closed.

The disc 5-9 is held in place and the entire unit formed by the varioustubular members and heating element is held in spaced relation to thecasing 4 by means of a nut and bolt structure 60 illustrated in detailin Figure 3. This structure comprises a reduced threaded portion 6!which extends through a central opening in disc 59 and which is threadedinto a hub 52 on a spider member 83. This spider member will be disposedin the forward end of tube 52 and is held therein by an inwardly curledforward end 64 thereof. The disc 5% is held in place by a shoulder 64formed by the enlarged portion 65 of the bolt structure. This enlargedportion 55 is threaded to receive a nut 65 which will be disposed withincasing as shown in Figure 1. A pair of washers Ell will be disposedbetween nut 66 and the end of the casing l. These washers will be ofmaterial which will not readily conduct heat. The member 58 has a squaremember 68 integrally formed thereon which fits within the square opening8 in the forward end of easing 4. This member it has a strip ofheat-insulating material extending entirely around the edge thereof. Theenlarged portion 55 will extend forwardly from the forward end of casingt as illustrated in Figure 1 and has a nut l6 threaded thereon. A washerii of heat-insulating material is disposed between the nut it! and theend of the casing 4. The extreme forward end of member 66 is reduced asindicated at 72 and is threaded to receive a substantially L-shaped pipeor nozzle 73. The inher portion of this nozzle or pipe 13 is of coneshape as indicated at "M so that it will fit tightly in openings ofvarious sizes.

The member 69 has an air passageway 15 extending entirely therethrough.The inner end of this passageway will communicate with the chamber wherethe heating element 3'1 is located.

The outer end thereof will communicate with a passageway I6 extendingthrough the nozzle or pipe member 13.

In assembling our device, the casing 4, of course, will be separate fromthe handle member I. The unit embodying the heating element and thevarious tubular members will be'assembled first. This will be done byplacing the inner tube member 42 in position with its rear end againstmember 39 and then positioning the ring member 45 as shown in Figure 1.positioned on the member 39, it will be apparent that the heatingelement will be mounted on this member 39 and the spider member 63 willbe positioned in the forwardend of the tubular member 42. Then thevarious tubular members will be disposed in their proper positions, thedisc 59 will be properly disposed and the rear end 6! of member 60 willbe threaded into the spider member 63. This will cause the varioustubular members to be tightly .held against disc 59 and ring 45 in anobvious manner.

The nut member 66 and washers 61 will then be mounted on the 'enlargedportion 65 of member 60. The entire unit so far formed and consisting ofthe various tubular members and the heating element together with member60 will then be positioned in casing 4 with member 60 extending throughthe opening 8. Then the handle member 1 will be brought almost intocooperative relation with casing 4 and the wires 40 will be connected.Then, the handle member and the casing will be fastened together. Thenut member 10 and washer H will then be-applied to the member 60 andadjusted into contact with the forward end of easing 4. 'Then', the pipemember 13 will be screwed into position on the member 60. It will beapparent that the square member 68 fitting within the square opening 8will prevent turning of member 60 during application or removal of pipe13. Thus, there will be no danger of turning the heating element so thatthe connecting wires thereof will be twisted loose and the electricalcircuit broken. It will be apparent that this device may be easilyassembled in a 'very satisfactory manner.

In the operation of this device, the L-shaped pipe or nozzle 13 isinserted in the opening of the gear case or other such member to whichit is desired to apply the heated air. illustrate diagrammatically howthis may be done. The pipe l3 will extend from the opening in the caseaconsiderable distance and may be directed towards the bottom of thecase so that all the hard or stifi grease or oil will be removed fromthe bottom thereof. Thecone-shaped member 14 on pipe 73 may be held incontact with the edge of the opening, regardless of its size, andpressure may be built up in the case if desired. If it is not desired tobuild up any appreciable amount of pressure in the case, the cone-shapedmember may be held loosely in the opening.

When the air' under pressure flows into the passageway H and thepassageway l4, it will move the plunger of the switch is forwardly andcomplete the circuit to the heating element 3? as previously described.The air will flow through the injector and will draw additional air intoour device from the atmosphere. By passing through the injector, the airunder pressure will be reduced in pressure and will then be dischargedinto the chamber within casing 4. Then it will flow forwardly until itpasses through openings 58 in the'outer tubular member and will passback and forth through the various .Before the member 42 is In Figure '7we r chambers as indicated by the air arrows in Figure 1. During passagethrough these various chambers the air will be preheated and it willfinally reach the chamber 48, surrounding the heating element 31. Itenters this chamber at the rear end thereof and then flows forwardlyalong the heating element and will be heated considerably during itspassage through this chamber. From the forward end of chamber 48, theair will flow through the passageway 15 in member 60 and then outthrough the passageway 16 in pipe 13. If air under pressure stopsflowing into passageways II and M, the plunger of the switch l5 will beimmediately returned by the spring to its rear position and willconsequently break the electrical circuit to the heating element,thereby rendering the heating element inoperative.

It will be apparent that the member 60 is effectively heat-insulatedfrom the outer casing 4. Also, since the member 39 at the rear ends ofthe tubular members and the heating element is composed ofheat-insulating material, there will be no danger of heat passing to theouter casing 4 through this member. Thus, the inner unit embodying thevarious tubular members and the heating element will be effectivelyinsulated from the outer casing land the handle member. Also, since themember 39 is flexible, it serves as a cushion which minimizes the effectof shocks and jars on the heating element.

It will be apparent from the preceding description that we have provideda device having many desirable features. This device is very simple instructure and can be readily assembled and, consequently, it can bemanufactured and sold at a comparatively low cost. Furthermore, thisdevice will function in a very eificient and satisfactory manner andwill be very economical in operation. Also, our device may be madepractically entirely of metal and will therefore be very sturdy, butsince the inner unit is efiiciently heat-insulated from the outer casingand handle member, there will be no danger of either the outer casing orthe handle member becoming so hot that the operator cannot handle thedevice. The heating element of our device is protected from shocks andjars. Also, we have provided a safety switch which is of such acharacter that it will render the heating element inoperative wheneverthere is no air under pressure flowing into our device or the pressurethereof falls below a predetermined degree. Consequently, there will beno danger of the heating element being operative while there is no airflowing through our device which would cause excessive heating of ourdevice and serious injury thereto.

Having thus described our invention, what we claim is:

1. An air heating gun comprising a handle member, a main hollow casingsecured to said handle member, said handle member having a passagewayextending therethrough and cornmunicating with the interior of said maincasing for conducing air under pressure thereinto, an air injectordisposed in said passageway through which the air under pressure mustpass before entering said casing, said injector being of such a typethat it will take in additional air from the atmosphere and will reducethe pressure of the air under pressure as it passes therethrough, anelectric heating element disposed within said casing, a plurality ofmetallic tubular members surrounding said heating element, said tubularand jars thereon, said tubular members being so arranged that the airentering said main casing must travel through all of said chambersbefore reaching said heating element, a tube leading from the chamber inwhich said heating element is disposed to a point outside of said maincasing, a nozzle member mounted on the outer end of said tube, a switchfor controlling said heating element, said switch being automaticallyoperable by the air under pressure which flows through said passagewayto cause the circuit to said heating element to be completed when airunder pressure is supplied to the gun and to be broken when the pressureof the air supplied to the gun falls below a predetermined degree.

2. An air heating gun comprising a handle member, a main hollow casingsecured to said handle member, means for conducting air under pressureinto said main casing, an air injector through which the air underpressure must pass before entering said casing, said injector being ofsuch a type that it will take in additional air from the atmosphere andwill reduce the pressure of the air under pressure as it passestherethrough, an electric heating element disposed within said casing, aplurality of tubular members surrounding said heating element, saidtubular members being of various diameters, means for maintaining thevarious tubular members in spaced relation so that a plurality ofchambers surrounding said heating element are formed, each of saidtubular members having openings adjacent one end thereof, the openingsin one tubular member being formed therein adjacent the end opposite tothat of. the adjacent tubular member in which the openings thereof areformed, said tubular members being so arranged that the air enteringsaid main casing must travel through all of said chambers beforereaching said heating element, means for conducting the air from thechamber in which said heating element is disposed to a point outside ofthe main casing, a switch for controlling said heating element, saidswitch being automatically operable by the air under pressure whichflows to the main casing to cause the circuit to said heating element tobe completed when air under pressure is supplied to the gun and to bebroken when the pressure of the air supplied to the gun falls below apredetermined degree.

3. An air heating device comprising a main hollow casing, means forconducting air under pressure into said main casing, an air injectorthrough which the air under pressure must pass before entering saidcasing, said injector being of such a type that it will take inadditional air from the atmosphere and will reduce the pressure of theair under pressure as it passes therethrough, an electric heatingelement disposed within said casing, a plurality of tubular memberssurrounding said heating element and being of various diameters, meansfor maintaining the various tubular members in spaced relation so that aplurality of chambers surrounding said heating element are formed, eachof said chambers being in communication with the adjacent chambers, saidtubular members being so arranged that the air entering said main casingmust travel through all of said chambers before reaching said heatingelement, a switch for controlling said heating element, said switchbeing automatically operable by the air under pressure which flows tothe main casing to cause the circuit to said heating element to becompleted when air under pressure is supplied to the device and to bebroken when the pressure of air supplied to the device falls below apredetermined degree.

4. An air heating gun comprising a handle member, a main hollow casingsecured to said handle member, said handle member having a passagewayextending therethrough and communicating with interior of said maincasing for conducting air under pressure thereinto, an air injectordisposed in said passageway through which the air under pressure mustpass before entering said casing, said injector being of such a typethat it will take in additional air from the atmosphere and will reducethe pressure of the air under pressure as it passes therethrough, anelectric heating element disposed within said casing, a plurality ofmetallic tubular members surrounding said heating element and being ofvarious diameters, means for maintaining the various tubular members inspaced relation so that a plurality of chambers surrounding said heatingelement are formed, each of said tubular members having openingsadjacent one end thereof, the openings in one tubular member beingformed therein adjacent the end opposite to that of the adjacent tubularmember in which the openings thereof are formed, all of said tubularmembers having polished surfaces so that they will readily reflect heat,said heating element having one of its ends supported on a flexiblemember in order to minimize shocks and jars thereon, said tubularmembers being so arranged that the air entering said main casing musttravel through all of said chambers before reaching said heatingelement, a tube leading from the chamber in which said heating elementis disposed, and a nozzle member mounted on the outer end of said tube.

5. An air heating gun comprising a handle member, a main hollow casingsecured to said handle member, means for conducting air under pressureinto said main casing, an air injector through which the air underpressure must pass before entering said casing, said injector being ofsuch a type that it will take in additional air from the atmosphere andwill reduce the pressure of the air under pressure as it passestherethrough, an electric heating element disposed Within said casing, aplurality of tubular members surrounding said heating element, saidtubular members being of various diameters, means for maintaining thevarious tubular members in spaced relation so that a plurality ofchambers surrounding said heating element are formed, each of saidtubular members having openings adjacent one end thereof, the openingsin one tubular member being formed therein adjacent the end opposite tothat of the adjacent tubular member in which the openings thereof areformed, said tubular members being so arranged that the air enteringsaid main casing must travel through all of said chambers beforereaching said heating element, and means for conducting the air from thechamber in which said heating element is disposed to a point outside ofthe main casing.

6. An air heating device comprising a main hollow casing, means forconducting air under pressure into said main casing, an air injectorthrough which the air under pressure must pass before entering saidcasing, said injector being of such a type that it will take inadditional air from the atmosphere and will reduce the pressure of theair under pressure as it passes therethrough, an electric heatingelement disposed within said casing, a plurality of tubular memberssurrounding said heating element and being of various diameters, meansfor maintaining the various tubular members in spaced relation so that aplurality of chambers surrounding said heating element are formed, eachof said chambers being in communication with the adjacent chambers, saidtubular members being so arranged that the air entering said main casingmust travel through all of said chambers before reaching said heatingelement.

7. An air heating gun comprising a handle member, a main hollow casingsecured to said handle member, said handle member having a passagewayextending therethrough and communicating with the interior of said maincasing for conducting air under pressure thereinto, an electric heatingelement disposed within said casing, a plurality of metallic tubularmembers surrounding said heating element, said tubular members being ofvarious diameters, means for maintaining the various tubular members inspaced relation so that a plurality of chambers sur rounding saidheating element are formed, each of said tubular members having openingsadjacent one end thereof, the openings in one tubular member beingformed therein adjacent the end opposite to that of the adjacent tubularmember in which the openings thereof are formed, all of said tubularmembers having polished surfaces so that they will readily reflect heat,said heating element having one of its ends supported on a flexiblemember in order to minimize shocks and jars thereon, said tubularmembers being so arranged that the air entering said main casing musttravel through all of said chambers before reaching said heatingelement, a tube leading from the chamber in which said heating elementis disposed to a point outside of said main casing, a nozzle membermounted on the outer end of said tube, a switch for controlling saidheating element, said switch being automatically operable by the airunder pressure which flows through said passageway to cause the circuitto said heating element to be completed when air under pressure issupplied to the gun and to be broken when the pressure of the airsupplied to the gun falls below a predetermined degree.

8. An air heating gun comprising a handle member, a main hollow casingsecured to said handle member, means for conducting air under pressureinto said main casing, an electric heating element disposed Within saidcasing, a plurality of tubular members surrounding said heating element,said tubular members being of various diameters, means for maintainingthe various tubular members in spaced relation so that a plurality ofchambers surrounding said heating element are formed, each of saidtubular members having openings adjacent one end thereof, the openingsin one tubular member being formed therein adjacent the end opposite tothat of the adjacent tubular member in which the openings thereof areformed, said tubular members being so arranged that the air enteringsaid main casing must travel through all of said chambers beforereaching said heating element, means for conducting the air from thechamber in which said heating element is disposed to a point outside ofthe main casing, a switch for controlling said heating element, saidswitch being automatically operable by the air under pressure whichflows to the main casing to cause the circuit to said heating element tobe completed when air under pressure is supplied to the gun and to bebroken when the pressure of the air supplied to the gun falls below apredetermined degree,

9. An air heating device comprising a main hollow casing, means forconducting air under pressure into said main casing, an electric heatingelement disposed within said casing, a plurality of tubular memberssurrounding said heating element and being of various dimeters, meansfor maintaining the various tubular members in spaced relation so that aplurality of chambers surrounding said heating element are formed, eachof said chambers being in communication with the adjacent chamber, saidtubular members being so arranged that the air entering said main casingmust travel through all of said chambers before reaching said heatingelement, a switch for controlling said heating element, said switchbeing automatically operable by the air under pressure which flows tothe main casing to cause the circuit to said heating element to becompleted when air under pressure is supplied to the device and to bebroken when the pressure of air supplied to the device falls below apredetermined degree.

19. An air heating gun comprising a handle member, a main hollow casingsecured to said handle member, means for conducting air under pressureinto said main hollow casing, an electric heating element disposedwithin said casing, a plurality of tubular members surrounding saidheating element, said tubular members being of various diameters, meansfor maintaining the various tubular members in spaced relation so that aplurality of chambers surrounding said heating element are formed, eachof said chambers being in communication with the adjacent chamber, saidtubular members being so arranged that the air entering said main casingmust travel through all of such chambers before reaching said heatingelement, said heating element having one of its ends supported on aflexible member in order to minimize shocks and jars thereon, a tubeleading from the chamber in which said heating element is disposed to apoint outside of said main casing, and a nozzle member on the outer endof said tube.

11. An air heating device comprising a main hollow casing, means forconducting air under pressure into said main casing, an electric heatingelement disposed within said casing, a plurality of wall memberssurrounding said heating element and being disposed in spaced relationso that a plurality of chambers surrounding said heating element areformed, each of said chambers being in communication with the adjacentchamber and being so arranged that the air entering said main casingmust travel through all of said chambers before reaching said heatingelement, a switch for controlling said heating element, said switchbeing automatically operable by the air under pressure which flowsthrough the main casing to cause the circuit to said heating element tobe completed when air under pressure is supplied to the device and to bebroken when the pressure of air supplied to the device falls below apredetermined degree.

12. An air heating device comprising a main hollow casing, means forconducting air under pressure into said main casing, an air injectorthrough which the air under pressure must pass before entering saidcasing, said injector being of such a type that it will take inadditional air from the atmosphere, an electric heating element disposedwithin said casing, a plurality of wall members surrounding said heatingelement and being disposed in spaced relation so that a plurality ofchamberssurrounding said heating element are formed, each of saidchambers being in communication with the adjacent chamber and being soarranged that the air entering said main casing must travel through allof said chambers before reaching said heating element.

13. An air heating device comprising a main hollow casing, means forconducting air under pressure into said main casing, an air injectorthrough which the air under pressure must pass before entering saidcasing, said injector being of such a type that it will take inadditional air from the atmosphere, an electric heating element disposedwithin said casing, means for permitting the heated air to flow fromsaid casing, and a switch for controlling said heating element, saidswitch being automatically operable by the air under pressure whichflows through the main casing to cause the circuit to said heatingelement to be completed when air under pressure is supplied to thedevice and to be broken when the pressure of the air supplied to thedevice falls below a predetermined degree.

14. An air heating gun comprising a main,

from place to place with the hands, means for U conducting air underpressure into said main casing, an air injector through which the airunder pressure must pass before entering said casing, said injectorbeing of such a type that it will take in additional air from theatmosphere and will reduce the pressure of the air under pressure as itpasses therethrough, an electric heating element disposed within saidcasing, said casing being provided with a passageway of much smallercross-sectional area than the main casing for permitting the heated airto flow from said casing, and means for operating said heating element.

THOMAS J. TULLY.

ROBERT B. JACKSON.

